With recent rapid development of digital cameras and mobile phones equipped with cameras, further downsizing and increase in the pixel count of the solid-state image sensing device have been required. In solid-state image sensor, a color resist material is provided between optical sensor section and condenser lens to selectively guide the light having the desired wavelength to the optical sensor section. The downsizing and increase in the pixel count of the solid-state image sensor are associated with the problem of decrease in light collecting (condensing) efficiency and sensitivity. Accordingly, transparent pixels and partitions having a high refractive index are formed in the same layer as the color resist material for efficient light collection to thereby avoid decrease in the device sensitivity. Typical methods used for preparing such pixel or partition include processing of an inorganic film deposited by CVD or the like by dry etching and processing of the film formed by coating a resin. Formation of a material with the refractive index of 1.65 to 2.00 optimal for the lens or the optical waveguide is difficult by the former method, and therefore, the latter method has become the focus of attention.
So far, there have been proposed, for example, a photosensitive siloxane composition containing a polysiloxane compound, a quinone diazide compound, a solvent, and a thermally crosslinkable compound (see, for example, Patent Document 1), a negative photosensitive resin composition containing a polymer having carboxyl group and/or phenolic hydroxy group and ethylenically unsaturated double bond group, a photo-radical polymerization initiator, and a compound having at least 3 groups each containing an unsaturated carboxylate ester structure having hydroxy group in one molecule (see, for example, Patent Document 2), a material having a high refractive index containing a siloxane compound having an aromatic hydrocarbon group (see, for example, Patent Document 3). However, it has been difficult to form a cured film having the high refractive index required for the material used for the lens used in CMOS image sensor from these materials. In view of such situation, particles of metallic compounds such as titanium oxide and zirconium oxide are generally added in the transparent lens materials for the CMOS image sensor for the purpose of improving the refractive index. For example, there have been disclosed a positive photosensitive resin composition containing polyamic acid, a compound having phenolic hydroxy group, a quinone diazide compound, and inorganic particles (see, for example, Patent Document 4) and a silicone copolymer containing silsesquioxane having a phenol unit and a fused polycyclic hydrocarbon group (see, for example, Patent Document 5). These materials, however, suffered from loss of transparency due to the coloring in the curing by polyamic acid or phenolic hydroxy group.
Known materials having a high refractive index and transparency that have been disclosed include a coating composition containing an organosilane, a siloxane oligomer, and metal oxide fine particles and/or sol (see, for example, Patent Document 6) and a siloxane resin composition prepared by copolymerizing a metal oxide particle with an alkoxysilane (see, for example, Patent Document 7). Most of such materials are non-photosensitive, and therefore, they are subjected to patterning by wet etching using a chemical solution or by dry etching using plasma.
Also disclosed are siloxane resin compositions with positive photosensitivity having high refractive index and transparency (see, for example, Patent Document 8). However, solvent resistance of the cured film is not fully realized by the low temperature curing at 200 to 220° C., and curing at a higher cure temperature has been necessary. In the meanwhile, siloxane resin compositions with negative photosensitivity having high refractive index and transparency have also been proposed, and examples include a compound containing silica-coated titanium oxide particles and at least 2 acryloyl groups, photopolymerization initiator composition (see, for example, Patent Document 9), reaction product of an inorganic oxide fine particles and an alkoxysilane compound, inorganic oxide fine particles, and a photopolymerization initiator composition (see, for example, Patent Document 10). These compounds, however, had the problem that they were incapable of forming check pattern and rectangular pattern having the desired high taper angle when they were used for the formation of pixels or partitions, and there has been a demand for materials exhibiting both of these properties.